The present invention relates generally to joints for bell or socket and spigot-type pipe couplings and, more particularly, to an improved joint for use in retaining the spigot end of a first pipe within the socket or bell end of a second pipe against the separating forces encountered due to internal fluid pressures in the pipe line.
Various types of restrained mechanical pipe joints are known. A typical mechanical pipe joint is shown in U.S. Pat. No. 4,506,919. The mechanical pipe joint shown in that patent requires that a ring be fixed by welding onto the outer surface of the spigot end of a pipe. The spigot end of such pipe is held by a retainer ring which has a internal sloped surface bearing against the ring welded to the spigot end of the first pipe. The retainer ring itself is held to the flange of the socket end of a second pipe by bolts. Upon the tightening of such bolts, the retainer ring bears against the ring welded to the spigot end of the first pipe thereby pulling the spigot end of the first pipe into the socket end of the second pipe thereby completing the restrained mechanical pipe joint.
A shortcoming of such restrained mechanical pipe joints is that they require a ring to be welded to the outside of the spigot end of a pipe. It is desirable to provide a restrained mechanical pipe joint useful to join the spigot end of a first pipe to the socket end of a second pipe without the need of welding a ring about the spigot end of the first pipe. Frequently, pipe must be cut in the field, and it is desirable to be able to insert such field cut pipe into the socket end of other pipe and form a joint between the two pipes without the need for field welding of a ring onto a pipe end.